The present invention relates to an ignition apparatus for a multi-cylinder reciprocating internal combustion engine, and more particularly to an ignition apparatus for a multi-cylinder reciprocating internal combustion engine having a plurality of spark plugs for each cylinder, in which the sparking of at least a selected one of said plurality of spark plugs may be effectively disabled.
Heretofore, a conventional reciprocating internal combustion engine has had a single spark plug for each cylinder. In recent years, however, under a special condition in which, for example, the use of lean air-fuel mixture in a combustion chamber is required in order to suppress the amount of NOx in the exhaust gas below a predetermined amount, a plurality of, for example, two, spark plugs have been used for each cylinder in order to solve the problem of instability of combustion. Such technology is known as a 1-cylinder 2-plug system and shown in the U.S. Pat. No. 3,809,402, U.S. Pat. No. 3,935,844 and U.S. Pat. No. 3,964,454.
In the multi-cylinder reciprocating internal combustion engines, such as a 1-cylinder, 2-plug system internal combustion engine, having a plurality of spark plugs for each cylinder, it is desired to switch the operation mode such that one spark plug is operated for each cylinder under a normal condition while two plugs are operated for each cylinder under a special condition. In order to switch the operation mode a transistorized ignition apparatus may be used, for example, to control the operation of a power transistor which controls the primary current of an ignition coil by a switching signal. Namely, a power transistor for driving a selected one of the two spark plugs for each cylinder is disabled under normal conditions but enabled only under the special conditions, while another power transistor for driving the other spark plug is always enabled. In this case, when the power transistor for driving the selected one spark plug is switched from the disabled state to the enabled state, no problem occurs but a problem occurs in the opposite case. That is, when the operation of a power transistor which controls the primary current of an ignition coil is stopped at any time point, a high voltage may be unexpectedly generated in the secondary of the ignition coil so that a spark may occur at the associated spark plug at an undesired time point other than a normal ignition timing. As a result, the operability is deteriorated and the durability of the engine is lowered.